Diabetes is a typical lifestyle-related disease, and when its symptoms worsen, risks of inducing complications such as retinopathy, nephropathy, and neuropathy increase, symptoms of apoplexy and ischemic cardiopathy develop or intensify, and the patient's QOL (Quality of Life) and life prognosis are significantly impaired. Diabetes is classified into type 1 diabetes whose onset occurs in children or youth, and type 2 diabetes whose onset occurs in adults. Type 1 diabetes is attributed to complete destruction of cells (langerhans-islet β cells of pancreas) that produce insulin, which is a blood glucose lowering hormone, and, as a result, it is known to cause erratic fluctuation of blood glucose level and various disorders. Hitherto, treatment of type 1 diabetes has depended on insulin reinforcement therapy in which insulin is administered. However, it is difficult to stably control blood glucose only through insulin administration, and, in some cases, the risk increases for acute hypoglycemic attack accompanied by a serious altered state of consciousness. Furthermore, insulin administration is merely a symptomatic therapy for type 1 diabetes, and its inability to be a fundamental cure is a problem.
As a result, in recent years, islet transplantation in which islets are removed from a pancreas of a donor for transplantation is attracting people's attention as a fundamental therapy for type 1 diabetes. Islets are injected into a portal vein of a patient through islet transplantation enter the liver, survive in portal veins all around the liver, and start secreting insulin, making it possible to fundamentally cure type 1 diabetes. Since islet transplantation is performed by drip transfusion of langerhans islets (pancreatic islets), an abdominal operation is not necessary and pancreatic juice treatment is also unnecessary; thus, when compared to whole pancreas transplantation from a brain-dead donor, which is a general organ transplantation, islet transplantation have advantages of being highly safe and having an extremely small burden on the patient.
On the other hand, islet transplantation has a problem in which transplanted islets have a poor graft survival rate and transplantation of islets obtained only from a single donor is insufficient. Therefore, with hitherto known islet transplantation, multiple donors are required for a single recipient. Furthermore, since isolated islets perish in several days outside a living body, islets isolated from a donor have to be transplanted, immediately. Furthermore, currently with hitherto known islet transplantation, insulin independent rate (proportion of recipients that do not require insulin administration) five years after transplantation in the follow-up stage becomes as low as approximately 10%. As described above, due to factors such as low graft survival rate of transplanted islets, large quantity of islets required for transplantation, and low insulin independent rate, islet transplantation has a problem of being inferior in terms of long-term outcome when compared to whole pancreas transplantation which is a highly invasive procedure for recipient.
In recent years, as a technique for increasing islets' graft survival rate in islet transplantation, a mix-transplantation, in which islets that are to be transplanted are admixed with bone marrow-derived mesenchymal stem cells (BMSC), is proposed (cf. Non-Patent Literature 1). However, this technique has drawbacks such as (1) an immunosuppressant is administered when performing the mix-transplantation, (2) a large number of BMSCs are combined, (3) the actual effect of islet transplantation cannot be evaluated since a pouch using greater omentum is formed at a site for transplantation and large quantities of islets+BMSCs are transplanted thereto, and (4) there is no reduction in the quantity of islets administered through allotransplantation.
If the quantity of to-be-transplanted islets for islet transplantation can be reduced and isolated islets can live and be cultured for an extended period of time, it becomes possible to transplant islets obtained from a single donor to multiple recipients. In such a case, it is expected that islet transplantation will rapidly spread and can greatly contribute to diabetes treatment. However, hitherto, such a technique had not been established.